Golf ball compositions including microcellular materials and methods for making same

ABSTRACT

This invention is directed to golf balls including one or more foamed, microcellular materials. The invention also encompasses methods of controlling or adjusting one or more material properties or the weight distribution of a golf ball, and methods of forming golf balls including such microcellular materials.

FIELD OF INVENTION

[0001] The present invention is directed to golf balls and golfball-forming microcellular materials, and to methods for forming suchgolf balls and of controlling material properties and weightdistribution of golf balls formed of such materials.

BACKGROUND OF THE INVENTION

[0002] Conventional golf balls can be divided into several generalclasses: (a) solid golf balls having one or more layers, and (b) woundgolf balls. Solid golf balls include one piece balls, which are easy toconstruct and relatively inexpensive, but have poor playingcharacteristics and are thus generally limited for use as range balls.Two-piece balls are constructed with a generally solid core and a coverand are generally the most popular with recreational golfers becausethey are very durable and provide maximum distance. Balls having atwo-piece construction are commonly formed of a polymeric core encasedby a cover. Typically, the core is formed from polybutadiene that ischemically crosslinked with zinc diacrylate and/or other similarcrosslinking agents. These balls are generally easy to manufacture, butare regarded as having limited playing characteristics. Solid golf ballsalso include multi-layer golf balls that are comprised of a solid coreof one or more layers and/or a cover of one or more layers. These ballsare regarded as having an extended range of playing characteristics.

[0003] Wound golf balls are generally preferred by many players due totheir high spin and soft “feel” characteristics. Wound golf ballstypically include a solid, hollow, or fluid-filled center, surrounded bya tensioned elastomeric material and a cover. Wound balls generally aremore difficult and expensive to manufacture than solid two-piece balls.

[0004] Golf ball performance characteristics are typically described interms of their distance, durability, spin and feel. Thesecharacteristics need not be mutually exclusive, and yet golf balls thathave a suitable feel, such as those with balata covers, tend not to beextraordinarily durable. This is because materials that have hightensile and compressive strengths often diminish the compressibility ofthe balls into which they are incorporated, and thus they generally feelhard. There thus exists a need for resilient and durable materials thatmay be used to form golf ball covers, mantle layers, and centers thatretain the soft feel desired by many golfers.

[0005] Numerous attempts have been made to provide such materials. Forexample, U.S. Pat. Nos. 4,274,637 and 4,431,193 disclose covers andmantle layers, respectively, made of cellular, or foamed ionomermaterials. These materials, which are lighter than the solid materialsfrom which they are made, are produced with blowing agents, nucleatingagents, and other additives that thermally decompose at hightemperatures to form bubbles within a polymer melt. Foamed materialsmade in this manner are hereinafter referred to as “conventional foams.”

[0006] U.S. Pat. No. 5,824,746 discloses golf balls covers comprisingfoamed, metallocene-catalyzed polymers. These polymers were also formedusing conventional blowing or foaming agents.

[0007] The use of foamed materials can alter the coefficient ofrestitution of a golf ball, which is generally indicative of itsresiliency. Resiliency, which is regulated by the U.S. Golf Association,is measured by the “Initial Velocity Test,” wherein a golf ball isstruck by a club face moving at a speed of approximately 146 feet persecond. Once struck by the club face, the velocity of the ball ismeasured. The maximum prescribed limit for a golf ball tested in thismanner is 250+2% ft/s at 75° F.

[0008] Conventional foams typically include about 10³ to 10⁶ cells/cm³,with the cells averaging about 100 μM or larger in diameter. It is thislarge average size and an uneven cell size distribution that arebelieved to account for the relatively poor mechanical properties ofconventional foams. See, e.g., Behravesh, A. H., et al., Antec '98Conference Proceedings, vol. II, pp. 1958-1967 (Apr. 26-30, 1998).Consequently, golf balls including conventional foams are expected to beinferior compared to those that do not include such conventional foams.

[0009] A further limitation of conventional foams is that they cannot beused to form materials thinner than the average cell size of about 100μM. This limitation restricts the applications in which foamed materialsmay be used. In addition, the conventional foams require chemicalblowing agents, which may produce some environmental concerns.

[0010] A material property of conventional foams can be modified orimproved by the use of microcellular materials. These materials are madeby exposing a polymer melt to a gas under high pressure, and thenquickly removing that pressure. The resulting cells are smaller, morenarrowly distributed with regard to size, and occur in higher densitiesthan those of conventional foams. Until recently, however, microcellularmaterials were made primarily from simple, single component polymermelts, such as polystyrene.

[0011] For example, U.S. Pat. No. 4,473,665 discloses microcellularclosed cell foams made from polystyrene, polycarbonate, polyester,nylon, or a thermoplastic material, and a method of making such foams.Also disclosed are closed cell sizes on the order of 2 to 25 microns, aswell as the addition of fillers such as carbon black to control voidsize.

[0012] U.S. Pat. No. 5,160,674 discloses microcellular foams ofamorphous or semi-crystalline polymers, such as polyethylene orpolypropylene, having bubbles on the order of 5 to 25 microns indiameter with bubble density of approximately 10¹⁰ bubbles/cm³.

[0013] Recently, reports have begun to surface in the literature ofmicrocellular materials made from mixtures of polymeric and othercompounds such as cellulose fiber. See, e.g., Barlow, C., et al., Antec'98 Conference Proceedings vol. II, pp. 1944-1948 (Apr. 26-30, 1998);and Matuana, L. M. et al., Antec '98 Conference Proceedings vol. II, pp.1968-1975 (Apr. 26-30, 1998).

[0014] U.S. Pat. No. 5,181,717 discloses an inflated bladder-type sportsor leisure ball, e.g., a football, that includes an external layer ofpolyurethane or polyurethane-polyurea foam with compact integral skin.The foamed layer is microalveolate or microcellular at its core, with acompact skin and an intermediate zone between the core and skin withprogressively smaller cells towards the skin.

[0015] WO 99/63019 discloses microcellular thermoplastic elastomericpolymeric structures having an average cell size less than 100 μm indiameter. These materials may be formed from a thermoplastic elastomericolefin, preferably metallocene-catalyzed polyethylene, with articledensities ranging from less than 0.5 g/cm³ to less than 0.3 gm/cm³.

[0016] U.S. Pat. No. 6,037,383 discloses microcellular polyurethaneelastomers having improved dynamic properties based on an isocyanateconsisting essentially of 4,4′-MDI.

[0017] Despite these disclosures of microcellular materials, however,Applicants are not aware of any disclosures that include suchmicrocellular materials in golf balls. Thus, the need still exists toproduce components with material properties modified by the use ofmicrocellular materials.

SUMMARY OF THE INVENTION

[0018] This invention is directed to microcellular golf ball-formingmaterials for one-piece, two-piece, and multi-layer (i.e., three or morelayers) golf balls, such as golf balls that are fluid-filled, includeone or more wound layers, include a multi-layer cover, and the like.

[0019] In particular, the invention encompasses a golf ball including atleast one core layer and at least one cover layer disposed over the atleast one core layer, with the at least one cover layer having athickness of at least about 0.03 inches, wherein at least one of thecore layers or cover layers is formed of a microcellular compositionhaving an average cavity density of about 10⁵ cavities/cm³ to 10¹⁴cavities/cm³, and an average cavity diameter of less than about 100microns. In one embodiment, the cover has at least one of a dimplecoverage of greater than about 60 percent, a hardness from about 35 to80 Shore D, or a flexural modulus of greater than about 500 psi, and thegolf ball has at least one of a compression from about 50 to 120 or acoefficient of restitution of greater than about 0.7.

[0020] The microcellular composition preferably has an average cavitydiameter from about 0.1 microns to 95 microns, more preferably fromabout 5 microns to 50 microns. The microcellular composition can furtherinclude at least one of a stabilizer, crosslinking agent, pigment,brightener, lubricant, or density-adjusting filler. In particular, themicrocellular composition preferably includes a polymer selected fromthe group of thermoplastics, thermoplastic elastomers, rubbers,thermosets, and mixtures thereof.

[0021] In one embodiment, the microcellular composition includes apolymer having a hardness of at least about 15 Shore A, a flexuralmodulus of at least about 500 psi, a density of at least about 0.3g/cm³, and a rebound of at least about 30%. In another embodiment, thepolymer includes at least one of a copoly(ether-ester),copoly(ether-urethane), copoly(ester-urethane), copoly(ether-amide), ormetallocene-catalyzed polymer.

[0022] As noted above, any type of golf ball construction may be formedaccording to the invention. In one embodiment, at least one of the corelayers includes the microcellular composition. In another embodiment,the core layers include at least one center layer including a fluid andat least one intermediate layer including the microcellular compositiondisposed about the at least one center layer. In yet another embodiment,the golf ball has at least two core layers including a first core layerincluding a tensioned elastomeric material wound about a second corelayer including the microcellular composition. The microcellularcomposition can be included to modify the density and/or moment ofinertia of the golf ball or portions thereof. The moment of inertia ofthe golf ball should typically be from about 0.3 to 0.9 g/cm².

[0023] The invention also relates to a golf ball having an Atticompression of at least about 50 and a coefficient of restitution of atleast about 0.7 at 125 ft/sec that includes a solid core having adeflection of about 1 mm to 6 mm under a load of 100 kg, and at leastone cover layer disposed over the core and being formed of amicrocellular composition having an average cavity density of about 10⁵cavities/cm³ to 10¹⁴ cavities/cm³, and an average cavity diameter ofless than about 100 microns.

[0024] The invention also encompasses a golf ball having an Atticompression of at least about 50 and a coefficient of restitution of atleast about 0.7 at 125 ft/sec that includes a core, an inner cover layerdisposed over the core and being formed of a microcellular compositionhaving an average cavity density of about 10⁵ cavities/cm³ to 10¹⁴cavities/cm³, and an average cavity diameter of less than about 100microns, and an outer cover layer disposed over the inner cover layerand having a flexural modulus of about 10,000 psi to 70,000 psi.

[0025] Methods of forming such golf balls are also encompasses by theinvention. In one embodiment, a method of adjusting at least onematerial property or weight distribution of a golf ball includes atleast partially melting a polymeric material, saturating the meltedpolymeric material with a gas at a first pressure sufficient tosubstantially uniformly distribute the gas through the melted polymericmaterial, shaping the gas-saturated polymeric material at an elevatedpressure to prevent substantial cell nucleation within the material,sufficiently reducing the first pressure, in the absence of sonicvibration, and supersaturating the shaped polymer material with a gas sothat the polymer material is modified to form a substantially uniformlynucleated shaped microcellular polymeric material having closed-cell,microcellular voids having a diameter of no greater than about 100microns, solidifying the microcellular polymer material sufficiently toinhibit formation of additional voids, and incorporating themicrocellular polymeric material into a golf ball.

[0026] The polymeric material is preferably selected from the group ofthermoplastics, thermoplastic elastomers, rubbers, thermosets, andmixtures thereof. In a preferred embodiment, the polymeric material iscombined with at least one additive before being exposed to the gas. Theat least one additive typically includes a stabilizer, crosslinkingagent, pigment, brightener, lubricant, density-adjusting filler, or acombination thereof.

[0027] The method preferably uses a gas that includes air, a noble gas,nitrogen, carbon dioxide, or a mixture thereof. The gas flow rate istypically at least about 0.005 lbs./hr.

[0028] The incorporating into a golf ball can include forming themicrocellular composition into portion of a golf ball core, anddisposing a dimpled outer cover over the core so as to form the golfball. In one embodiment, the forming includes forming the microcellularcomposition into a golf ball center, and providing at least one mantlelayer over the center. In the alternative, the incorporating step caninclude forming a golf ball core, and forming a material including themicrocellular composition into at least a portion of a golf ball cover.In another embodiment, the forming includes at least one of injectionmolding, compression molding, reaction injection molding, or casting themicrocellular composition. In yet another alternative, the golf ball canbe a one-piece golf ball formed of a material including themicrocellular composition.

[0029] This invention is also directed to a method of affecting theweight distribution within a golf ball. In this embodiment, the momentof inertia may be adjusted by varying the type and density of themicrocellular materials of the invention. For example, a golf ball canbe prepared having a moment of inertia from about 0.3 g/cm² to 0.9g/cm². In another embodiment, this invention encompasses a method ofmodifying the material properties of the golf ball components. Thismethod includes the incorporation of a microcellular material into agolf ball as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further features and advantages of the invention can beascertained from the following detailed description that is provided inconnection with the drawings described below:

[0031]FIG. 1 illustrates a golf ball having a single core layer and asingle cover layer according to the invention;

[0032]FIG. 2 illustrates a golf ball having three layers according tothe invention; and

[0033]FIG. 3 illustrates a multi-layer golf ball according to theinvention.

DEFINITIONS

[0034] As used herein, the term “Atti compression” is defined as thedeflection of an object or material relative to the deflection of acalibrated spring, as measured with an Atti Compression Gauge, that iscommercially available from Atti Engineering Corp. of Union City, N.J.Atti compression is typically used to measure the compression of a golfball. When the Atti Gauge is used to measure cores having a diameter ofless than 1.680 inches, it should be understood that a metallic or othersuitable shim is used to make the measured object 1.680 inches indiameter.

[0035] As used herein, the terms “cell,” “cavity,” “void,” and “bubble”each refer to a region within a material that is not filled by thatmaterial. The “cell” may contain another material or may be a void, butpreferably the cell contains a gas, typically air.

[0036] As used herein, the term “diameter” when used to describe a cellrefers to the average distance between opposing boundaries of that cell,and does not imply that the cell is spherical in shape.

[0037] As used herein, the term “microcellular material” means amaterial including cells having average diameters of less than 100 μm,and in particular to material including cells having average diametersfrom about 0.1 μm to 95 μm in diameter on average and a density fromabout 10⁵ cells/cm³ to 10¹⁴ cells/cm³, preferably from about 10⁷cells/cm³ to 10¹⁰ cells/cm³.

[0038] As used herein, the terms “conventional foamed material” and“conventional foam” mean a cellular material that is not a microcellularmaterial, e.g., has cells with an average diameter of greater than 100μm. Examples of conventional foamed materials include those described inU.S. Pat. No. 4,274,637.

[0039] As used herein, the term “cover” means the outermost portion of agolf ball. A cover typically includes at least one layer and may containindentations such as dimples and/or ridges. Paints and/or laminates aretypically disposed about the cover to protect the golf ball during usethereof.

[0040] As used herein, the term “core” means the innermost portion of agolf ball, and may include one or more layers. When more than one layeris contemplated, the core includes a center and at least one mantlelayer disposed thereabout. At least a portion of the core, typically thecenter, is solid or fluid. The core may also include one or more woundlayers including at least one tensioned material wound about the center.

[0041] As used herein, the term “mantle layer” means a portion of a golfball positioned between the center and cover of a golf ball. The mantlelayer is also sometimes referred to as an inner cover layer or anintermediate layer in the golf ball art.

[0042] As used herein, the term “fluid” means a gas, liquid, gel, paste,or the like, or a combination thereof.

[0043] As used herein, the terms “polymer” and “polymeric material”include amorphous, semi-crystalline, or crystalline polymers, andmixtures thereof, including, for example, random and block copolymers,rubbers, thermoplastics, thermoplastic elastomers, and the like.

[0044] As used herein, the term “compatible blend” means a blend of twoor more polymers that is heterogeneous on a microscopic scale, buthomogeneous on a macroscopic scale, and has useful golf ball properties.

[0045] The term “about,” as used herein in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range.

DETAILED DESCRIPTION OF THE INVENTION

[0046] This invention is directed to golf balls and golf ball-formingcompositions including one or more microcellular materials. Thecompositions of the present invention possess numerous advantages overconventional golf ball-forming compositions, including lower materialcosts, lighter weight, and potential improvements in materialsproperties. The compositions of this invention may be formed without thenucleating agents used to make conventional foamed materials, andpossess smaller cavities of more narrowly distributed sizes than thoseof conventional foamed materials. Materials made from the compositionsof this invention, and the resultant golf balls incorporating suchmaterials, are expected to be more durable than materials made ofconventional foams.

[0047] The materials of this invention may be made with nucleatingagents, but are preferably made without such agents. As noted herein,the golf balls of the invention are formed from materials that includethermoplastic polymers, thermoset polymers such as polybutadiene, ormixtures of such polymers and/or copolymers. Further, these materialsmay include ingredients such as, but not limited to, stabilizers,crosslinking-agents, pigments, brighteners and other such additives,such as reinforced glass fibers, etc. The microcellular materials ofthis invention can be used to form materials thinner than conventionalmaterials, since the cell sizes are no greater than 100 μm.

[0048] The microcellular material compositions of this invention maythus be used to form any part of a dual- or multi-layer golf ball,including its center, mantle layer(s) and cover. Preferably, themicrocellular material compositions are used to form part of the core,i.e., the center or one of a plurality of optional mantle layersdisposed between the center and cover. Consequently, this invention isfurther directed to golf balls including microcellular materials andmethods of forming the same. The golf balls incorporating including amicrocellular material may be one-piece, two-piece, or multi-layer golfballs, although the golf balls are preferably two-piece or multi-layergolf balls. The golf balls of this invention provide numerous advantagesover conventional golf balls, which typically include lower materialcosts and modified material properties. It should be noted, however,that the present invention does contemplate golf balls includingcombinations of both microcellular and conventional foamed materials.

[0049] The compositions of the invention allow the golf ballmanufacturer to adjust the density or mass distribution of the ball intowhich they are incorporated, thereby affecting resiliency, spin rate,and performance. When at least a portion of the golf ball core or centeris formed from a microcellular material, a density-adjusting fillermaterial can be added to, e.g., the cover or the mantle, to distributethe mass of the ball towards the outer surface to adjust the angularmoment of inertia of the golf ball. Similarly, when a microcellularmaterial is used to form at least a portion of the cover, adensity-adjusting filler material can be added to part of the core todecrease the angular moment of inertia of the ball. Alternatively, whena microcellular material is used to form at least a portion of a mantlelayer, a density-adjusting filler material can be added to either thecover or the center, or both. This invention is thus further directed toa method of adjusting the weight distribution within a golf ball byincorporating one or more microcellular materials into a desired portionof a golf ball.

[0050] The compositions of this invention may be made according to themethods disclosed by U.S. Pat. Nos. 4,473,665 and 5,160,674, both ofwhich are incorporated herein in their entirety by express referencethereto. Other methods of producing microcellular materials are wellknown to those of ordinary skill in the art, and include commercialprocessing means such as the nucleation device disclosed by WO 97/06935,as well as the processes described by PCT Publications WO 99/32543; WO99/32544; WO 98/31521; and WO 98/08667. Moreover, U.S. Pat. No.6,037,383, for example, discloses microcellular polyurethane elastomersand other materials suitable for use in the present invention to formgolf balls incorporating microcellular compositions.

[0051] During the microcellular material forming process, the gas flowrate is typically at least about 0.005 lbs./hr. In one embodiment, thegas flow rate is from about 0.02 to 0.2 lbs./hr. A mold temperature ofat least about 30° F. is typically used. The microcellular processgenerally occurs as follows:

[0052] 1. A supercritical fluid (SCF) of an atmospheric gas is injectedinto the polymer through a barrel to form a single-phase solution, withthe SCF delivery system, screw, and injectors designed to allow forrapid dissolution;

[0053] 2. A large number of nucleation sites, which are present inorders of magnitude greater than conventional foaming processes, areformed where controlled cell growth occurs by using a large and rapidpressure drop to help create uniformity in this process;

[0054] 3. Cells are expanded by diffusion of gas into the bubbles; and

[0055] 4. Mold design is used to control the shape of the part asdesired.

[0056] For example, a semi-crystalline polymer material is typicallyselected and heated above the melting point thereof; the melted polymermaterial is saturated with a substantially uniformly or uniformconcentration of gas; the gas-saturated polymer material is shaped in acavity, mold, or die at an elevated pressure to substantially preventcell nucleation within the material; uniform or substantially uniformbubble formation in the polymer is initiated in the absence of sonicvibrations by reducing the pressure and supersaturating the polymer withgas resulting in a uniform or substantially uniform nucleated shapedpolymer material having closed-cell, microcellular voids having anaverage diameter of no greater than 100 microns; and the temperature ofthe polymer material is lowered below the melting point of the materialto inhibit or prevent further cell growth.

[0057] The compositions of this invention include any polymer or mixtureof polymers suitable for incorporation into a golf ball. The particularpolymer or mixture of polymers will depend upon the proposed use of thecomposition, i.e., durable and rigid polymers will typically be chosenwhen the composition is used to form covers, while softer polymers andrubbers will typically be used in compositions used to form one or moreoptional mantle layers and/or the center. Consequently, suitablepolymers for use in forming microcellular materials for incorporationinto a golf ball may be readily selected by one of ordinary skill in theart, and include the following exemplary polymers: homo and copolymersof polystyrene, polyethylene, polypropylene, polyester, thermoplastic orthermoset polyurethane, polyamide, polycarbonate, urea, epoxy,poly(ethylethylene), poly(heptylethylene), poly(hexyldecylethylene),poly(isopentylethylene), poly(butyl acrylate), poly(2-ethylbutylacrylate), poly(heptyl acrylate), poly(2-methylbutyl acrylate),poly(3-methylbutyl acrylate), poly(N-octadecylacrylamide),poly(octadecyl methacrylate), poly(butoxyethylene),poly(methoxyethylene), poly(pentyloxyethylene),poly(1,1-dichloroethylene), poly(cyclopentylacetoxyethylene),poly(4-[(2-butoxyethoxy)methyl]styrene), poly(4-dodecylstyrene),poly(4-tetradecylstyrene), poly(phenethylmethylethylene),poly[oxy(allyloxymethyl)ethylene], poly[oxy(ethoxymethyl)ethylene],poly(oxyethylethylene), poly(oxytetramethylene), poly(oxytrimethylene),poly(oxycarbonylpentamethylene),poly(oxycarbonyl-3-methylpentamethylene),poly(oxycarbonyl-1,5-dimethylpentamethylene), poly(silanes) andpoly(silazanes), and main-chain heterocyclic polymers, as well as theclasses of polymers to which they belong. The microcellular material mayalso be formed from a combination of one or more of these or othersuitable polymers disclosed herein.

[0058] This invention also contemplates the use of metallocene-catalyzedpolymers and polymer blends, such as those disclosed by U.S. Pat. No.5,824,746, which is incorporated herein by express reference thereto.Consequently, compositions of the present invention may includecompatible blends of at least one metallocene-catalyzed polymer and atleast one ionomer that are formed using any blending method available tothose of ordinary skill in the art. Typical metallocene-catalyzedpolymer blends include compatible blends of metallocene polymers andionomers, such as ethylene methacrylic acid ionomers, ethylene acrylicacid ionomers, and their terpolymers, sold commercially under the tradenames SURLYN® and IOTEK® by E.I. DuPont deNemours of Wilmington, Del.,and Exxon Corporation of Irving, Tex., respectively.

[0059] The polymer component of the compositions of this invention mayalso include any thermoplastic or thermoplastic elastomer (TPE) orthermoset. Exemplary TPEs suitable for use in the present inventioninclude block copoly(ether- or ester-esters), block copoly(ether- orester-amides), copoly(ether- or ester-urethanes), polystyrene TPEs, andmixtures, isomers and derivatives thereof.

[0060] Suitable commercially available copoly(ester-ether) TPEs includethe HYTREL® series from DuPont, which includes HYTREL® 3078, G3548W,4056, G4069W and 6356; the LOMOD® series from General Electric Companyof Pittsfield, Mass., which includes LOMOD® ST3090A and TE3055A;ARNITEL® and URAFIL® from Akzo of Saint Louis, Ill.; ECDEL® from EastmanKodak of Rochester, N.Y.; and RITEFLEX® from Hoechst Celanese of CorpusChristi, Tex. In a preferred embodiment, the thermoplastic elastomerincludes HYTREL® 3078.

[0061] Suitable block copoly(ether-amide) TPEs are described by U.S.Pat. No. 4,331,786, which is hereby incorporated herein in its entiretyby express reference thereto. Suitable commercially availablethermoplastic copoly(amide-ethers) include the PEBAX® series fromElf-Atochem of Philadelphia, Pa., which includes PEBAX® 2533, 3533, 4033and 6333; the GRILAMID® series by Emser Industries of Sumpter, S.C.,which includes ELY 60; and VESTAMID® and VESTENAMER® by Creanova Inc. ofPiscataway, N.J. (formerly known as Hüls America Inc.).

[0062] Suitable block copoly(ether-urethane) TPEs include alternatingblocks of a polyurethane oligomer. The polyurethane block may include adiisocyanate, typically 4,4′-diphenylmethane diisocyanate,4,4′-dicyclohexylmethane diisocyanate, 2,4-toluene diisocyanate,2,6-toluene diisocyanate, para-phenylene diisocyanate or mixturesthereof, chains extended with a diol such as 1,4-butanediol, a dithiolsuch as 1,4-butanedithiol, a thio-substituted alcohol, such as1-thiolbutane-4-ol, or mixtures thereof. Optionally, the blockcopoly(urethane) copolymer can be at least partially included of atleast one dithioisocyanate.

[0063] Suitable block copoly(ester-urethane) TPEs include the ESTANE®series, which includes ESTANE® 58133, 58134, 58144 and 58311 andsuitable block copoly(ether-urethane) TPEs include ESTANE® 58810, 58881,5740X955, 5740X820, 5740X946, all of which are commercially availablefrom the B.F. Goodrich Company; the PELLETHANE® series commerciallyavailable from Dow Chemical of Midland, Mich., which includesPELLETHANE® 2102-90A and 2103-70A; ELASTOLLAN® commercially availablefrom BASF of Budd Lake, N.J.; DESMOPAN® and TEXIN® commerciallyavailable from Bayer of Pittsburgh, Pa.; Q-THANE® commercially availablefrom Morton International of Chicago, Ill.; and PANDEX from Dannippon ofJapan.

[0064] Block polystyrene TPEs suitable for use in this invention includeblocks of polystyrene or substituted polystyrene, e.g., poly(α-methylstyrene) or poly(4-methyl styrene) chemically linked or joined to theends of lower softening point blocks of either an unsaturated orsaturated rubber. Unsaturated rubber types typically include butadiene,which can form styrene-butadiene-styrene (hereafter “SBS”) blockcopolymers, or isoprene, which can form styrene-isoprene-styrene(hereafter “SIS”) block copolymers, silicone rubber, blalata,styrene-butadiene rubber (“SBR”), and the like. Examples of suitablecommercially available thermoplastic SBS or SIS copolymers include theKRATON® D series from Shell Corporation of Houston, Tex., which includesKRATON® D2109, D5119 and D5298; VECTOR® from Dexco of Plaquemine, La.;and FINAPRENE® from Fina Oil and Chemical of Plano, Tex.

[0065] Suitable microcellular materials are typically those having ahardness of at least about 15 Shore A, a flexural modulus of at leastabout 500 psi, a density of at least about 0.3 g/cm³, and a rebound ofat least about 30%.

[0066] In addition to the polymer component, the compositions of thisinvention preferably include one or more additives or other ingredients.Particularly contemplated are those frequently found in golf ballcompositions, including crosslinking agents, free-radical initiators,lubricants, pigments, brighteners, density-adjusting fillers, and thelike, or combinations thereof, in amounts and ratios either known orreadily determined by those of ordinary skill in the art. If anucleating agent is used to form the final composition of the invention,it preferably should not react with any of these ingredients in a waythat weakens or decomposes the final composition to such a degree thatrenders it unsuitable for incorporation into a golf ball.

[0067] Suitable crosslinking agents include, for example, metal saltdiacrylates, dimethacrylates, and monomethacrylates wherein the metal ismagnesium, calcium, zinc, aluminum, sodium, lithium or nickel.Preferably, the crosslinking agent is zinc diacrylate, more preferablyzinc diacrylate containing less than about 10% zinc stearate.

[0068] Although not required, a free-radical source, often alternativelyreferred to as a free-radical initiator, may be included in thecompositions of this invention. The free-radical initiator component ispreferably included when the microcellular material will be incorporatedinto a golf ball center or mantle layer. The free-radical initiator maybe any compound, or combination of compounds, present in an amountsufficient to initiate a crosslinking reaction to facilitatecrosslinking of the polymer component of the composition. Thefree-radical initiator is preferably a peroxide, and more preferably anorganic peroxide. Suitable free-radical initiators include, for example,di(2-t-butyl-peroxyisopropyl)benzene peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxy)valerate on calcium silicate, laurylperoxide, benzoyl peroxide, t-butyl hydroperoxide, and mixtures thereof.In a preferred embodiment, the free radical initiator is aninhibitor-containing peroxide, such as 2,6-di-t-butylbenzoquinone,2,6-di-t-butyl-4-methylene-2,5-cyclohexadiene-1-one,2,6-di-t-butyl-4-hydroxybenzaldehyde, 2,6-di-t-butyl-4-isopropylphenol,4,4′-methylene bis-(2,6-di-t-butylphenol),1,2-bis-(3,5-di-t-butyl-4-hydroxyphenyl)ethane,2,3,5,6-tetramethylbenzoquinone, 2-t-butyllhydroquinone,2,2′-methylenebis-(4-methyl-6-t-butylphenol), and the like, and mixturesthereof. The free-radical initiator is typically present in an amountgreater than about 0.1 parts per hundred of the polymer component,preferably about 0.1 to 15 parts per hundred of the polymer component,and more preferably about 0.2 to 5 parts per hundred of the totalpolymer component. The free-radical source may alternatively oradditionally be one or more of an electron beam, UV or gamma radiation,x-rays, or any other high energy radiation source capable of generatingfree radicals. It should be further understood that heat oftenfacilitates initiation of the generation of free radicals when peroxidesare used as a free-radical initiator.

[0069] The golf ball compositions of this invention may also includedensity-adjusting fillers such as zinc oxide, barium sulfate, metallicpowders, and regrind (such as recycled core molding matrix ground toabout 30 mesh particle size). Density-adjusting fillers are typicallyadded to conventional golf ball core compositions to adjust the densityand/or specific gravity of the core or portions thereof, and may besimilarly included in the golf balls of the present invention.

[0070] The use of density-adjusting fillers in the present invention isoptional, however, because the characteristics of the microcellularmaterial prepared according to the invention can preferably used in thisinvention to adjust the density of a material or the moment of inertiaof the ball as a whole, for example, modifying the cellular density andcell size of the microcellular material to adjust the moment of inertia.The moment of inertia of a golf ball is calculated as the sum of theproducts formed by multiplying the mass (or sometimes the area) of eachelement of a figure by the square of its distance from a specified line,such as the center of each component of a golf ball. This property isdirectly related to the radius of gyration of a golf ball, which is thesquare root of the ratio of the moment of inertia of a golf ball about agiven axis to its mass. It has been found that the greater the moment ofinertia, or the farther the radius of gyration is to the center of theball, the lower the spin rate of the ball. By varying the weight, size,and density of the components of the golf ball, the moment of inertiacan be modified to adjust the ball characteristics, such as the spinrate. For example, the ball can be prepared using the microcellularmaterials of the invention, optionally with density-adjusting fillers,to provide a moment of inertia that is typically from about 0.3 g/cm² to0.9 g/cm². In one embodiment, the moment of inertia of the golf ball canbe from about 0.35 g/cm² to 0.55 g/cm², while in one preferredembodiment, it can be from about 0.4 g/cm² to 0.5 g/cm². Thus, the golfball typically has a specific gravity in the core from about 0.7 to 15,preferably from about 0.8 to 5, more preferably from about 0.9 to 2.When the core has a center and at least one intermediate layer, theintermediate layer typically has a specific gravity from about 0.7 to12, preferably from about 0.8 to 5, more preferably from about 0.9 to 2.In one embodiment, the mantle as whole has a specific gravity no greaterthan 1.2, while in another the specific gravity is no less than 1.2.

[0071] The compositions of this invention may also include antioxidantsthat prevent elastomer breakdown. Useful antioxidants include quinolinetype antioxidants, amine type antioxidants, and phenolic typeantioxidants and the like, and mixtures thereof. Suitable types andamounts of antioxidant may be readily selected by one of ordinary skillin the art.

[0072] Other ingredients, such as accelerators, e.g.,tetramethylthiuram, processing aids, processing oils, plasticizers,dyes, and pigments, may also be used in the methods and compositions ofthe present invention. Metals such as titanium, copper, and tungsten mayalso be added. Suitable amounts of such ingredients may be readilydetermined by one of ordinary skill in the art without undueexperimentation.

[0073] It is preferred that each composition of this invention be madeby mixing and combining its ingredients over a period of time and at atemperature suitable to produce a mixture of desired consistency andhomogeneity. At this point, the mixture is exposed to a gas at apressure and for a time sufficient for the gas to permeate the mixture.The pressure is then rapidly decreased in a manner sufficient to formcavities within the mixture that have an average diameter preferablyfrom about 2 μm to 95 μm, more preferably from about 4 μm to 70 μm, andmost preferably from about 5 μm to 50 μm. Suitable gases are preferablyinert, and include, for example, air, one or more noble gases, nitrogenand carbon dioxide. Suitable pressures and times for such processes maybe readily determined by those of ordinary skill in the art,particularly with reference to the literature and U.S. Pat. Nos.4,473,665 and 5,160,674. The type of gas, gas pressure, length ofpressurization, temperature, and the polymer component itself may all bevaried to obtain microcellular materials with a variety of differentdensities, hardnesses, and resiliencies suitable for incorporation intogolf balls.

[0074] As those of skill in the art are well aware, these and othervariables depend, for example, upon the polymer or mixture of polymerswithin a given composition. To be specific, polymers with lower meltingpoints are preferably foamed at lower temperatures so that decompositiondoes not occur. Temperature, time and pressure may also depend upon thechemical stability and reactivities of any crosslinking agents,free-radical initiators, antioxidants, or other optional ingredientsthat may be incorporated within the composition.

[0075] In another embodiment, a polymer, optionally combined with otheringredients, is converted into a microcellular material under conditionssuch as those described above, after which it is combined withadditional ingredients. This method is particularly appropriate for theformation of microcellular compositions using nucleating agents that mayreact unfavorably with other reactive ingredients that are included inthe polymer component, such as antioxidants.

[0076] Microcellular compositions can be readily incorporated into agolf ball, or a portion thereof, by any suitable golf ball formingmethod available to those of ordinary skill in the art. For example,while any portion of a golf ball may be made from the microcellularcompositions disclosed herein, solid spherical centers may also beprepared from conventional compositions by any available method, such ascompression molding, injection molding, reaction injection molding,co-injection molding, or casting techniques, preferably in a concentricfashion to maintain a substantially spherical center conventionalmethod, such as compression or injection molding. A fluid-filled centermay alternatively be formed instead of a solid center. Any additionallydesired center layers may then be added to the center by conventionalcompression or injection molding techniques, including reactioninjection, co-injection, or casting techniques, preferably in aconcentric fashion to maintain a substantially spherical center. Themantle layer(s) may also be applied by any suitable method available tothose of ordinary skill in the art.

[0077] The intermediate layer, or mantle layer, may be formed of anymaterial available to those of ordinary skill in the art, such as athermoplastic thread material. When thread is included in anintermediate layer, it preferably includes an elastomeric, polymericmaterial. Exemplary polymers include polyisoprene, polyether urea, suchas LYCRA, polyester urea, polyester block copolymers such as HYTREL,isotactic-poly(propylene), polyethylene, polyamide, poly(oxymethylene),polyketone, poly(ethylene terephthalate) such as DACRON,poly(acrylonitrile) such as ORLON, and trans-diaminodicyclohexylmethaneand dodecanedicarboxylic acid. LYCRA, HYTREL, DACRON, KEVLAR, and ORLONare available from E.I. DuPont de Nemours & Co. of Wilmington, Del.

[0078] Any conventional material or method may also be used in preparingthe golf ball cover, which is typically disposed over the center orcore. For example, as is well known in the art, ionomers, balata, andurethanes are all suitable golf ball cover materials. A variety of lessconventional materials may also be used for the cover, e.g.,thermoplastics such as ethylene- or propylene-based homopolymers andcopolymers. These homopolymers and copolymers may also includefunctional monomers such as acrylic and methacrylic acid, fully orpartially neutralized ionomers and their blends, methyl acrylate, methylmethacrylate homopolymers and copolymers, imidized aminogroup-containing polymers, polycarbonate, reinforced polycarbonate,reinforced polyamides, polyphenylene oxide, high impact polystyrene,polyether ketone, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene, acrylic-styrene-terephthalate, poly(ethyleneterephthalate), poly(butene terephthalate), poly(ethylene-vinylalcohol), poly(tetrafluoroethylene), and the like. Any of these polymersor copolymers may be further reinforced by blending with a wide range ofdensity-adjusting fillers, including glass fibers or spheres, ormetallic powders. The selection of a suitable cover, and applicationthereof over the mantle described herein, will be readily determinableby those of ordinary skill in the art, particularly in view of thedisclosure herein.

[0079] When golf balls are prepared according to the invention, theytypically will have dimple coverage greater than about 60 percent,preferably greater than about 65 percent, and more preferably greaterthan about 70 percent. As measured by ASTM method D-790, the flexuralmodulus of the cover material for use on the golf balls is typicallygreater than about 500 psi, and is preferably from about 500 psi to150,000 psi. The hardness of the cover material is typically from about35 to 80 Shore D, preferably from about 40 to 78 Shore D, and morepreferably from about 45 to 75 Shore D.

[0080] The resultant golf balls typically have a coefficient ofrestitution of greater than about 0.7, preferably greater than about0.75, and more preferably greater than about 0.78. The golf balls alsotypically have an Atti compression of at least about 40, preferably fromabout 50 to 120, and more preferably from about 60 to 100. Additionally,any unvulcanized rubber, such as polybutadiene, used in golf ballsprepared according to the invention typically has a Mooney viscositygreater than about 20, preferably greater than about 30, and morepreferably greater than about 40. Mooney viscosity is typically measuredaccording to ASTM D-1646.

[0081] Referring to FIG. 1, a golf ball 10 of the present invention caninclude a core layer 12 and a cover layer 16 surrounding the core layer12. In this embodiment, the core layer or the cover layer, or both, isformed from a material that includes the microcellular composition ofthe invention. Referring to FIG. 2, a golf ball 20 of the presentinvention can include two core layers 22 and 24, and a cover layer 26.In an alternative embodiment that depends on the thicknesses andmaterials used in each layer as will be readily understood by those ofordinary skill in the art, FIG. 2 depicts a single core layer 22, innercover layer 24, and an outer cover layer 26. In either embodiment, amaterial including a microcellular composition of the invention isincorporated into one or more of the layers in FIG. 2. Referring to FIG.3, a golf ball 30 of the present invention can include a plurality ofcore or cover layers. For example, the core layer 32 can befluid-filled, in which case core layer 34 is a shell, optionally foamed,to contain the fluid therein. In one embodiment with the fluid-filledcenter, core layer 36 includes a tensioned elastomeric material and acover layer 38 is disposed about the core layer 36. In anotherembodiment with a fluid-filled core layer 32, layer 36 is an inner coverlayer and layer 38 is an outer cover layer. In yet another embodimentwith a fluid-filled core layer 32, core layer 36 is a solid or foamedmaterial and a cover layer 38 is disposed thereon. Alternatively, theinnermost core layer 32 can be solid, one of core layers 34 and 36includes a tensioned elastomeric material, and cover layer 38 isdisposed thereabout. Although FIG. 3 shows only layers between theinnermost core layer and the outermost cover layer, it will beappreciated that any number or type of intermediate core layers may beused, as desired. In FIG. 3, the microcellular composition of theinvention could be included in any of the depicted layers, or in anycombination of such layers.

EXAMPLES

[0082] The following examples are only representative of the methods andmaterials for use in golf ball compositions and golf balls of thisinvention, and are not to be construed as limiting the scope of theinvention in any way.

Examples 1-16 Comparative Microcellular Material Characteristics

[0083] Fifteen sample materials were prepared for use according to theinvention and one corresponding conventional material was prepared forcomparison as noted below.

[0084] Microcellular materials were prepared by forming solid and foamedplaques of approximately 0.06 inches thickness of 57 weight percentpolyetherester (HYTREL 3078), 20 weight percent of an n-butyl acrylateand ethylene methacrylic acid copolymer (NUCREL 960), and 23 weightpercent zinc oxide. The injection molded foamed parts were made under100 tons of clamp pressure with cycle times from approximately 13 to 28seconds. The nitrogen gas flow rate was approximately 0.02 to 0.08lbs./hr., with the best results generally occurring with a flow rate of0.04 to 0.06 lbs./hr. These flow rates typically resulted inmicrocellular materials having a content of approximately 0.11 percentto 0.2 percent nitrogen by weight.

[0085] Flexural Modulus

[0086] A 1 in.×2 in. sample was cut from each of five plaques. The widthand thickness of each sample were measured in triplicate and averagedand the flexural modulus was measured according to ASTM D-790, TestMethod 1, although the samples were measured as received rather thanbeing conditioned. The average flexural modulus and standard deviationsare reported in the table below.

[0087] Tensile Properties

[0088] Samples as received were die-cut and tested for tensileproperties according to ASTM D638-97.

[0089] Density

[0090] Approximately 2 grams of each sample was weighed in air using ananalytical balance according to ASTM D297. The samples were also weightsuspended on a thin wire in reagent alcohol with a previously determineddensity, and the density was then calculated.

[0091] Shore Hardness

[0092] A 1 in.×2 in. sample was cut from each of five plaques. Thehardness was measured using Shore A and D durometers using ASTM D2240.

[0093] The flexural modulus, tensile properties, density, and hardnessvalues, as described above, are reported in Table I: TABLE I MATERIALPROPERTIES OF MICROCELLULAR COMPOSITIONS Flow Transverse Tensile NewDensity Melt Mold Avg. Cell Avg. Cell Tensile Tensile Yield Tensile Ex.Density Reduction Temp Temp Size Size Shore A Shore D Flex Mod. ModulusStrength, Stress, Strain @ # (g/cm³) (%) (F) (F) (microns) (microns)Hardness Hardness (KSI) KSI KSI KSI Break, %  1   1.109 12.7 455 to 8050  60 90.5 34.3 21.05 8.65 0.99 0.85 117.24 490 (0.5) (0.6) (0.32)(1.15) (0.04) (0.04) (9.37)  2   0.971 23.6 460 to 65 50  70 81.2 25.410.06 9.17 1.15 1.04 135.40 490 (0.5) (0.5) (0.20) (1.90) (0.10) (0.13)(33.35)  3   0.929 26.9 440 to 90 50 100 76.9 23.8 9.34 7.28 1.25 1.07212.69 455 (1.1) (0.80) (0.43) (0.15) (0.02) (0.04) (16.43)  4   1.1668.3  440 to 50 70  90 90.1 32.4 20.20 11.78 1.43 1.10 159.12 455 (0.4)(1.1) (0.66) (0.52) (0.04) (0.03) (13.90)  5   1.170 7.9  450 to 50 30 40 89.5 34.3 16.55 8.38 1.28 1.10 153.02 460 (0.6) (0.6) (4.13) (1.84)*(0.28)* (0.26)* (39.75)*  6   1.138 10.5 435 to 50 30  60 90.8 34.822.18 12.32 1.84 1.62 109.00 445 (0.2) (0.3) (0.36) (1.05) (0.04) (0.06)(17.11)  7   0.984 22.6 435 to 50 30 100 79.3 24.5 10.09 7.68 1.32 1.04223.91 445 (0.6) (0.7) (0.30) (0.57) (0.04) (0.05) (20.75)  8   0.99921.4 435 to 50 50  60 87.6 30.2 16.48 8.74 1.35 1.10 222.42 445 (0.8)(0.7) (2.46) (1.36)* (0.08)* (0.07)* (76.66)*  9   0.930 26.8 425 to 5050 100 84.1 29.4 14.79 7.61 1.14 0.95 173.58 435 (3.5) (2.1) (3.88)(1.99) (0.28) (0.26) (51.76) 10   0.816 35.8 445 to 120  50  60 73.522.4 11.26 8.98 1.14 0.87 86.04 480 (3.5) (1.6) (4.51) (1.71)* (0.02)*(0.09)* (46.27)* 11   1.114 12.4 425 to 50 50 100 82.2 26.7 10.68 8.111.67 1.14 380.82 450 (2.3) (1.0) (1.49) (0.47) (0.06) (0.04) (18.25)12   1.015 20.1 425 to 50 40 100 86.9 31.1 12.61 7.61 1.44 1.04 323.99450 (1.3) (0.5) (0.41) (0.72) (0.12) (0.06) (48.41) 13   1.037 18.4 425to 50 15  60 82.5 27.0 11.08 6.70 1.50 1.13 380.43 450 (1.1) (0.5)(0.32) (0.14) (0.01) (0.05) (10.18) 14   1.011 20.5 445 to 50 50 10086.3 30.5 13.23 5.93 0.98 0.78 178.03 480 (0.4) (0.3) (0.14) (0.51)(0.01) (0.02) (7.24) 15   0.98  22.6 490 to 130 20  20 84.2 26.0 10.795.42 0.52 0.51 76.79 500 (0.9) (1.4) (1.44) (1.25) (0.13) (0.13) (17.79)16** 1.271 0 N/A N/A 92.3 38.7 18.24 10.09 1.73 1.59 203.80 (0.3) (0.5)(2.09) (2.23) (0.07) (0.08) (6.36)

[0094] The foamed parts prepared had an average weight reduction of 16percent and a good surface and cell structure, with no blowouts. Areduction in hardness was achieved with all the microcellular foamedparts, with the best reductions in hardness being about 15 Shore Asofter and 18 Shore D softer. The cell size ranged from 15 to 70 micronsin the flow direction and 20 to 100 microns in the transverse direction.The surface appearance of the microcellular materials, the hardnessreductions, and the cell structure were all best with low mold and stocktemperatures. Each of these microcellular materials can be formed intoone or more layers of a golf ball, or blends of microcellularcomposition disclosed herein can be formed into one or more layers of agolf ball.

[0095] It is to be recognized and understood that the invention is notto be limited to the exact configuration as illustrated and describedherein. For example, it should be apparent that a variety of suitablematerials would be suitable for use in the composition or method ofmaking the golf balls according to the Detailed Description of theInvention. Accordingly, all expedient modifications readily attainableby one of ordinary skill in the art from the disclosure set forth hereinare deemed to be within the spirit and scope of the present claims.

What is claimed is:
 1. A golf ball comprising: at least one core layer;and at least one cover layer disposed over the at least one core layer,with the at least one cover layer having a thickness of at least about0.03 inches, wherein at least one of the core layers or cover layers isformed of a microcellular composition having an average cavity densityof about 10⁵ cavities/cm³ to 10¹⁴ cavities/cm³, and an average cavitydiameter of less than 100 microns.
 2. The golf ball of claim 1, whereinthe cover has at least one of a dimple coverage of greater than about 60percent, a hardness from about 35 to 80 Shore D, or a flexural modulusof greater than about 500 psi, and wherein the golf ball has at leastone of an Atti compression from about 50 to 120 or a coefficient ofrestitution of greater than about 0.7.
 3. The golf ball of claim 1,wherein the microcellular composition has an average cavity diameterfrom about 0.1 microns to 95 microns.
 4. The golf ball of claim 1,wherein the microcellular composition has an average cavity diameterfrom about 5 microns to 50 microns.
 5. The golf ball of claim 1, whereinthe microcellular composition further comprises at least one of astabilizer, crosslinking agent, pigment, brightener, lubricant, ordensity-adjusting filler.
 6. The golf ball of claim 1, wherein themicrocellular composition comprises a polymer selected from the groupconsisting of thermoplastics, thermoplastic elastomers, rubbers,thermosets, and mixtures thereof.
 7. The golf ball of claim 1, whereinthe microcellular composition has a hardness of at least about 15 ShoreA, a flexural modulus of at least about 500 psi, a density of at leastabout 0.3 g/cm³, and a rebound of at least about 30%.
 8. The golf ballof claim 7, wherein the polymer comprises at least one of acopoly(ether-ester), copoly(ether-urethane), copoly(ester-urethane),copoly(ether-amide), or metallocene-catalyzed polymer, or blendsthereof.
 9. The golf ball of claim 1, wherein at least one of the corelayers comprises the microcellular composition.
 10. The golf ball ofclaim 1, wherein the core layers include at least one center layercomprising a fluid and at least one intermediate layer comprising themicrocellular composition disposed about the at least one center layer.11. The golf ball of claim 1, wherein the golf ball comprises at leasttwo core layers including an outer core layer comprising a tensionedelastomeric material wound about an inner core layer comprising themicrocellular composition.
 12. The golf ball of claim 1, wherein thegolf ball has a moment of inertia from about 0.3 g/cm² to 0.9 g/cm². 13.A golf ball having an Atti compression of at least about 50 and acoefficient of restitution of at least about 0.7 at 125 ft/sec thatcomprises: a solid core having a deflection of about 1 mm to 6 mm undera load of 100 kg; and at least one cover layer disposed over the coreand being formed of a microcellular composition having an average cavitydensity of about 10⁵ cavities/cm³ to 10¹⁴ cavities/cm³, and an averagecavity diameter of less than about 100 microns.
 14. A golf ball havingan Atti compression of at least about 50 and a coefficient ofrestitution of at least about 0.7 at 125 ft/sec that comprises: a core;an inner cover layer disposed over the core and being formed of amicrocellular composition having an average cavity density of about 10⁵cavities/cm³ to 10¹⁴ cavities/cm³, and an average cavity diameter ofless than about 100 microns; and an outer cover layer disposed over theinner cover layer and having a flexural modulus of about 10,000 psi to70,000 psi.
 15. A method of adjusting at least one material property orweight distribution of a golf ball comprising: at least partiallymelting a polymeric material; saturating the melted polymeric materialwith a gas at a first pressure sufficient to substantially uniformlydistribute the gas through the melted polymeric material; shaping thegas-saturated polymeric material at an elevated pressure to preventsubstantial cell nucleation within the material; sufficiently reducingthe first pressure, in the absence of sonic vibration, andsupersaturating the shaped polymer material with a gas so that thepolymer material is modified to form a substantially uniformly nucleatedshaped microcellular polymeric material having closed-cell,microcellular voids having a diameter of no greater than about 100microns; solidifying the microcellular polymer material sufficiently toinhibit formation of additional voids; and incorporating themicrocellular polymeric material into a golf ball.
 16. The method ofclaim 15, wherein the polymeric material is selected from the groupconsisting of thermoplastics, thermoplastic elastomers, rubbers,thermosets, and mixtures thereof.
 17. The method of claim 15, furthercomprising combining the polymeric material with at least one additivebefore being exposed to the gas.
 18. The method of claim 17, wherein theat least one additive comprises a stabilizer, crosslinking agent,pigment, brightener, lubricant, or density-adjusting filler.
 19. Themethod of claim 15, wherein the gas comprises air, a noble gas, nitrogenor carbon dioxide.
 20. The method of claim 15, wherein the gas flow rateis at least about 0.005 lbs./hr.
 21. The method of claim 15, wherein theincorporating comprises: forming the microcellular composition intoportion of a golf ball core; and disposing a dimpled outer cover overthe core so as to form the golf ball.
 22. The method of claim 21,wherein the forming comprises: forming the microcellular compositioninto a golf ball center; and providing at least one mantle layer overthe center.
 23. The method of claim 21, wherein the forming comprises atleast one of injection molding, compression molding, reaction injectionmolding, or casting the microcellular composition.
 24. The method ofclaim 15, wherein the golf ball is a one-piece golf ball.